This invention relates to master-slave hydraulic linkages.
Hydraulic systems are known for transmitting motion at a distance. Since such systems operate on the principle that the hydraulic fluid is incompressible, many schemes have been proposed to compensate for unwanted changes in fluid volume, caused by such factors as temperature change, introduction of foreign matter, and fluid leakage, in order to keep the master and slave always synchronized. One such scheme, shown in Hebel et al., U.S. Pat. No. 3,363,418, utilizes pairs of oppositely acting check valves connecting a master cylinder to a reservoir kept under pressure, the valves acting either to release excess fluid or to make up for a fluid deficiency from the reservoir. Stark et al., U.S. Pat. No. 3,579,989, shows a similar scheme using a check valve and a pressure relief valve in parallel to vent or fill a master-slave circuit.
The systems described are generally for power steering applications. When it is desired to transfer rapidly reciprocating motion, up to 200 cycles per minute, to several locations, such as in the tooling of an indexing turret machine, it is desirable to move as little fluid as possible by having as small a piston diameter as possible and to have an easily controlled piston diameter in both directions. Conventional pistons with rods are difficult to build below 3/4 inch diameter, and because of the rod size requirement, the piston area on the head end is not the same as the area on the rod end. There is also the possibility of leakage past a conventional piston, causing lack of synchronization between master and slave. Also, it is desirable to insure that synchronization of master and slave is maintained on every stroke by having a compensation scheme that would operate effectively under rapid cycling. Compensation circuitry that remains inactive until needed is generally not reliable. Finally, it is desirable to use controllable fluid pressures to have protection against overload at the workpiece.
In transmitting reciprocating motion, pneumatic cylinders and mechanical linkages are also well known. Pneumatic cylinders require fairly complex control systems, including interlocks to prevent sticking valves, and at higher speeds (on the order of 2 linear feet per second), cushioned cylinders become ineffective in preventing impact, and it is necessary to add hydraulic snubbers to absorb impact. Cam driven mechanical linkages require many moving parts where the required motions are located at various points and at various angles in a machine. It would be desirable to transmit the positive motions of cams without needing a variety of different cranks, links, levers, and bearings.
Finally, the use of rod pistons in hydraulic systems is not, stated that broadly, new. However, their use has been in slow, high pressure applications where a heavy rod was desired and the rod was on the order of six inches in diameter.